1. Technical Field
The present invention relates to a printed circuit board and a method for manufacturing the same and more particularly, to a method for forming a resist layer protecting a circuit layer on a substrate having the circuit layer formed thereon.
2. Description of the Related Art
A printed circuit board (PCB), which is printed and formed with a line pattern, that is, a circuit layer on an electrical insulating substrate using a conductive material such as copper, is defined as a circuit board on which a mounted position of each electronic component is secured and the circuit layer connecting electronic components to each other is printed on a surface of the substrate and is fixed in order to densely mount many various kinds of electronic components on the substrate.
Examples of the printed circuit board include a single-sided printed circuit board in which the circuit layer is only formed on one surface of an insulating substrate, a double-sided printed circuit board in which the circuit layers are formed on both surfaces of the insulating substrate, and a multi-layer printed circuit board in which the circuit layers are formed as a multi-layer.
Meanwhile, the circuit layer disposed at an outmost layer of the printed circuit board is buried by a persistent protective film referred to as a resist and the resist is provided with a pattern corresponding to the circuit layer of the outmost layer. In order to accurately form the pattern on the resist, a resist layer method is widely used. Among others, resist layer methods of an alkali development type have mainly used in consideration of environmental issues or the like.
As one method of the resist layer methods, one-shot exposure method forming the pattern on a resist by first applying the resist onto the circuit layer and then by using a light from a lamp emitting an ultra violet ray has been widely known and has disclosed in Japanese Patent Laid-Open Publication No. Hei 01-141904, for example. In this collective exposure method, a photosensitive composition is applied onto a substrate and is dried, light from the lamp emitting the ultra violet ray is exposed onto the entire surface of the dried coating through a photomask, and development is then performed.
Meanwhile, the resist needs to have a thickness corresponding to the thickness of the circuit layer in order to insulate and protect the circuit layer. Therefore, in the case in which the thickness of the circuit layer is 100 μm or more, the thickness of the resist also needs to become 100 μm or more.
As described above, in the case in which the thickness of the resist is thick, the exposure and development conditions are needed to be intensified so as to be cured up to a lower portion of the resist in order to open the resist between the patterns of the circuit layer. However, due to the thick thickness of the resist, an upper portion of the resist is excessively cured and the lower portion thereof is relatively less cured. Therefore, as shown in FIG. 1, at the time of development, the lower portion of the resist 2 is over-developed, such that an undercut phenomenon occurs at the lower portion of the circuit layer 1. As a result, the lower portion of the circuit layer 1 is exposed.
In order to solve this problem, a method for applying thinner resist, exposing and developing the applied resist, and then repeating the above-mentioned processes several times to form one resist has been proposed. However, this method increases the number of processes in proportion to the times of laminating the resist, thereby degrading productivity and increasing processing cost. In addition, since the resist of the lowest layer is subjected to the phenomenon process in proportion to the times of laminating the resist, the lower portion of the circuit layer may be exposed similar to the related art.